Only God knows all the answers to this. However, I believe His reasons include: 1) To give each believer an introspective look at their lives as related to Jesus, so we can understand His Love for us; 2) to determine our positions of service to Him for eternity; 3) to give us crowns we will be able to then give to Him, thus an opportunity to demonstrate our worship and adoration of Him. I'm sure there is a lot more to it than this, but these are a few thoughts.